JP 2011-133502A discloses an externally-heating fixing device. The externally-heating fixing device directly heats the outer surface of a heating roller or a heating film. Specifically, the fixing device heats a fixing roller at a heating nip defined by the fixing roller and a heater, and fixes a toner image to a sheet at a pressure nip defined by the fixing roller and a pressure roller.
More specifically, the externally-heating fixing device includes a rotatable heater arm, a rotatable pressure roller arm, and a spring. The heater arm supports the heater. The pressure roller arm supports the pressure roller. The spring connects the heater arm and the pressure roller arm to each other. When the spring biases the heater arm and the pressure roller arm toward each other, the heater is pressed onto the fixing roller, forming the heating nip, and the pressure roller is pressed onto the fixing roller, forming the pressure nip. In the externally-heating fixing device, the heater arm and the pressure roller have the same leverages, and therefore the heating nip and the pressure nip have the same pressing forces.